Not to be argumentative, but RTA is the true meter, your ears are your measure of personal success.
I agree personal taste plays a big role in building a 'successful' car stereo. But lets also remember if we take that idea too far, we'd all still be bumping RoadGear and Pyramid because hey, it sounded good at the time.
And before anyone jumps down my throat, no Im not saying a flat RTA response is the desired setup for listening. Just saying there's been times I didn't realize I had an issue till the RTA told me, I solved it, and noticed an improvement. If you are a top ranked SQ tuner/installer, yeah you probably dont even need an RTA at all anymore. But most of us can still benefit highly from a meter that discerns the difference between accuracy and personal preference.
I like building systems that sound good to me, obviously. But I also like building systems that I feel anyone would enjoy, even a more experienced/critical listener. An RTA can help achieve that.
*gets off his soap box*